Banding
Visible steps or stripes in what should be a smooth change of colour.
Also: posterisation, colour banding
A sky that should fade evenly from pale to deep blue sometimes shows as a series of stripes. This is banding. It happens when there are too few colour levels to cover the range smoothly, because of low bit depth, heavy file compression or strong editing. Dark gradients are most at risk. Remedies are to work at a higher bit depth, to add a little noise or dithering, or to make the gradient cover a shorter range. In printing, the same word can mean stripes caused by a fault in the print head.